Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)3, which has the structure of Formula I:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
A ligand is referred to as “photoactive” when it is believed that the ligand contributes to the photoactive properties of an emissive material.
A first energy level (HOMO or LUMO) is considered “less than” or “lower” than a second energy level if it is lower on a conventional energy level diagram, which means that the first energy level would have a value that is more negative than the second energy level. A first energy level (HOMO or LUMO) is considered “higher” than a second energy level if it is higher on a conventional energy level diagram, which means that the first energy level would have a value that is less negative than the second energy level. For example, the HOMO of CBP −5.32 eV and the HOMO of TPBI is −5.70 eV, therefore the HOMO of CBP is 0.38 eV “higher” than the HOMO of TPBI. Similarly, the LUMO of mCP is −0.77 eV and the LUMO of CBP is −1.23 eV, therefore the LUMO of mCP is 0.46 eV “higher” than the LUMO of CBP. The above values were determined using density functional calculations performed using the Spartan 02 software package, available from Wavefunction Inc. of Irvine, Calif., at the B3LYP/6-31G* level. A pseudo potential option can be used for species containing heavy metals such as Ir(ppy)3. Density functional calculations have been demonstrated in the literature to be able to qualitatively predict energies of organic and inorganic compounds.
More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.
As used herein, the term “consisting essentially of” one or more materials as applied to a layer in an organic light emitting device means that there may be materials present in addition to those listed, but any such additional materials are present only in minor quantities (such as impurities) and do not significantly affect the electronic properties or emissive of the device, i.e., they do not significantly contribute to the transport or trapping of holes or electrons, they do not result in a shift of the recombination location, and they do not significantly contribute to or participate in exciton decay, emissive or otherwise.
Unless otherwise indicated, percentages of organic compounds in various layers described herein are weight percentages.
The following two references including Samuel as a co-author describe solution processable phosphorescent OLEDs with doped emissive layer in direct contact with ITO. E. E. Namdas, T. D. Anthopoulos, I. D. W. Samuel, Applied physics letters 86, 161104 (2005). T. D. Anthopoulos, M. J. Frampton, E. B. Namdas, P. L. Burn, I. D. W. Samuel, Adv. Mater. 2004, 16, No. 6, March 18, pp. 557-560.